Dissolved inorganic and organic phosphorus uptake in <i>Trichodesmium</i> and the microbial community: The importance of phosphorus ester in the Sargasso Sea

Abstract

The dynamics and relative importance of inorganic phosphate (P i ) and dissolved organic phosphorus (DOP) uptake were examined in Trichodesmium and the microbial community. Trichodesmium DOP and P i uptake rates were also compared to literature values from several other taxonomically important groups in the Sargasso Sea. Uptake rates and uptake kinetics of 33 P i and DOP (using alpha‐labeled adenosine‐5′‐triphosphate 33 P‐ATP as a model P ester compound) were assayed during two cruises. The in situ uptake rates suggest that the contribution of P ester to total P uptake can be greater than 25% for Trichodesmium , the microbial community, and key phytoplankton groups ( Prochlorococcus , Synechococcus , picoeukaryotes, and nanoeukaryotes), depending on the location. Based on the kinetics of P i uptake and P ester uptake, Trichodesmium is a poor competitor for P i but a much better competitor for P esters as compared to the microbial community. Trichodesmium growth rates calculated from the P i and P ester uptake parameters suggest that only a small fraction of the P ester pool needs to be bioavailable to allow reasonable growth rates. These data underscore the importance of P esters in supporting production by Trichodesmium in the Sargasso Sea, and provide the first in situ measurements of P ester uptake and uptake kinetics in this important N 2 ‐fixing genus.